UPDATE: As of Friday, October 5, 2018, Microsoft has now pulled Windows 10 1809 due to an overwhelming amount of reported bugs. See: Microsoft Removes Buggy Windows 10 1809 Upgrade
UPDATE October 5, 2018: Reported by some, Microsoft has delivered driver updates to their devices that have solved this problem.
It’s not just you and Windows 10 1809 is not destroying monitors, nor is it messing with display quality.
Confirmed now, for devices with certain Intel graphics hardware and drivers, the display resets to 50% brightness on reboot. We’ve yet to determine the exact models, but it appears to be happening in various scenarios. Additionally, installing a newer graphics driver from Intel does not resolve the issue.
For now, just reset the display to the brightness level you want until Microsoft delivers a fix for the problem.
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